The measurements were taken by the SPIRE spectrometer on board the European Space Agency’s Herschel Space Observatory. Far-infrared radiation from several regions in the nebula, including the neutron star at its centre, showed strong peaks at 618GHz and 1235GHz, corresponding to argon hydride ions containing argon-36. By contrast, the dominant argon isotope on Earth is argon-40, which is formed by the radioactive decay of potassium. The team’s observations back up calculations supporting the theory that the argon-36 isotope originates from massive supernova explosions in space.